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Old 12-04-2011, 02:16 PM   #1
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Default SCR Bridge Test While Running.

If you ever wanted to identify an SCR thats not firing on a bridge without taking the machine down and isolating the thyristors here is a pratical way to do this.
You can see the A-Phase SCR in forward is not conducting and affecting the forward C-Phase thyristor.
On the left is the before with the SCR not firing and the one on the right is the after with the SCR repaired.
SCR Bridge Test While Running.-bridge-before-after.jpg

Last edited by Mr.C; 12-04-2011 at 02:28 PM.
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Old 12-04-2011, 03:40 PM   #2
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If you have the proper test equipment, this is by far the easiest way to test SCRs.

Even a simple single-channel scope meter will do, but it takes a bit longer.
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Old 12-06-2011, 10:14 PM   #3
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I usually isolate with a 2 channel scope.
Out of curiosity, what was this bridge supplying?
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Old 12-13-2011, 07:53 PM   #4
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This can also be found using the frequency setting on a DVM. On a three phase full wave bridge the freq. will be 360 and 1/2 wave will be 180. Its been a long time but I believe you can find the problem thyristor by checking the freq. between the anode and cathode.
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Old 12-13-2011, 08:00 PM   #5
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Quote:
Originally Posted by KRP14AN
This can also be found using the frequency setting on a DVM. On a three phase full wave bridge the freq. will be 360 and 1/2 wave will be 180. Its been a long time but I believe you can find the problem thyristor by checking the freq. between the anode and cathode.
However you have 6 SCRs in each direction connected to the dc bus so how are you isolating? Perhaps you can expand for I am always looking for troubleshooting tips.
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